The standardized IEEE 802.11 Wireless LAN, WLAN, also referred to as a Wi-Fi network, is a wireless communications network technology that operates on unlicensed frequency bands. Currently, the standardized IEEE 802.11 WLAN operate mainly on the 2.4 GHz and/or the 5 GHz band. The standard specifications regulate the Physical, PHY, layer, Medium Access Control, MAC, layer, and other aspects of the nodes therein to secure their compatibility and inter-operability.
In the standardized IEEE 802.11 WLAN, a Basic Serving Set, BSS, is regarded the basic building block of the wireless communications network. The BSS comprise a number of nodes; normally, at least one Access Point, AP, and a number of stations, STAs, located within a certain coverage area or cell being served by the at least one AP. Here, it should also be noted that STAs that are located within an overlapping coverage area of two or more BSSs may also be referred to as STAs having an Overlapping Basic Service Set, OBSS.
Within a BSS/OBSS, the coordination of the transmissions between the at least one AP and the STAs is typically performed in a distributed manner using the Distribute Coordination Function, DCF. This means that before a transmission, a STA first performs a Clear Channel Assessment, CCA, by sensing the channel for a specific period of time. If the channel is deemed idle, then the STA transmits; otherwise, the STA typically has to wait a random back-off period and then again check whether the channel is idle and thus available for transmission. The random back-off period is commonly implemented by a back-off timer being set to a random time chosen uniformly between 0 and the current contention window, CW, size in the STA. The random back-off period also provides a collision avoidance mechanism for multiple STAs that wish to transmit in the same BSS. This may also be commonly referred to as Carrier Sensing Multiple Access with Collision Avoidance, CSMA/CA.
Additionally, this procedure for the coordination of the transmissions within the BSS/OBSS may further comprise a Request-To-Send/Clear-To-Send, RTS/CTS, exchange procedure. In this case, a transmitting node, e.g. AP or STA, requests access to the channel explicitly by sending a so-called RTS message and requires a reception of a so-called CTS message from the intended receiving node, e.g. AP or STA, before performing the data transmission. During the RTS/CTS message exchange, essentially all messages, i.e. RTS, CTS, Data and Control Signalling messages, which are transmitted will comprise a NAV timer value. The NAV time values specifies the remaining duration of the entire data packet transmission. Other nodes in the BSS/OBSS, e.g. APs or STAs, which also receives these messages will then set their internal NAV timer with a corresponding value. The internal NAV timer will then, while running, mark the channel as being busy.
One improvement that may be introduced in future WLAN standards is the adjustments of the sensing threshold for the Clear Channel Assessment, CCA. This sensing threshold may be referred to as the Clear Channel Assessment Threshold, CCAT. The CCAT is used to assess whether the channel is busy or idle in that the channel is deemed busy in case a received signal strength level of a transmission surpasses the CCAT, or deemed idle in case a received signal strength level of a transmission do not surpass the CCAT.
With the use of a static CCAT, a node in the BSS/OBSS may refrain from accessing the channel in case it is exposed to concurrent transmissions in neighbouring BSSs, even though simultaneous transmissions would be possible, i.e. the interference caused by the simultaneous transmissions on each other would be at a tolerable level. This has the disadvantage of limiting the number of simultaneous transmissions that may be performed in the BSS/OBSS at any given time. In turn, this will also limit the performance of the wireless communications network by not fully utilizing the available channel; especially, as the CCAT used today is conservatively set to the very low value, such as, e.g. −82 dBm.
Instead, if a node in the BSS/OBSS, i.e. STAs or APs, could dynamically and individually adapt its CCAT, then the amount of concurrent transmissions in the wireless communications network may be increased without significantly increasing the probability of collisions within the BSS/OBSS. In other words, the utilization of the channel would increase without a deterioration of the performance of the wireless communications network. Therefore, an adaptive channel access mechanism has been proposed IEEE 802.11-15/0132r8, “Specification Framework for TGax”.
In this adaptive channel access mechanism, each node in the BSS/OBSS may adaptively adjust its COAT depending on the current situation. Some studies have shown that adjusting the COAT to a more aggressive value, e.g. a higher value than −82 dBm, may provide an increase in throughput for both the mean and 5th percentile worst performing cell-edge nodes. However, while spatial reuse features in the WLAN may improve efficiency of the wireless communications network, it will also increase the interference level in the entire wireless communications network. The characteristic of this interference may be very time dynamic depending on the transmission pattern of the node causing the inference. Such time dynamic interferences brings challenges to the design of link adaptation and may cause high packet loss rate if the link adaptation fails to adjust the Modulation and Coding Scheme, MCS, according to the level of the interference. Consequently, this high packet loss rate may result in both reduced user throughput and higher transmission latency, which leads to a decrease in transmission performance in the wireless communications network.